1. Technical Field
The present invention relates to a driving device for an image display medium, more specifically, to a driving device for a repeatedly rewritable image display medium that displays an image by applying voltage between the substrates to move the colored particles.
2. Related Art
Conventionally, an image display medium that uses colored particles is known as a repeatedly rewritable image display medium having memory capability. Such image display medium is configured including for example, a pair of substrates, and plural types of particle groups of different color and charge property that are enclosed between the substrates so as to be movable between the substrates by the applied electric field. A gap member for partitioning the space between the substrates into plural cells is arranged between the substrates to prevent the particles from concentrating at one region of the substrate and the like.
In such image display medium, the voltage corresponding to the image is applied between the pair of substrates to move the particles, and the image is displayed as a contrast of the particles of different color. The particles remain adhered to the substrate by van der Waals' force or image force even after the application of the voltage is stopped, thereby maintaining the image display.
The response (mobility) of the particles with respect to the applied voltage depends on the time (pulse width) in which the voltage is applied or the voltage value. The response with respect to the applied voltage significantly differs between the particles that are adhered to the substrate and the particles that are stripped from the substrate and that have started moving.
In other words, the conditions of the application voltage necessary to move the particles in a stationary state (state the particles adhered to the substrate and in a stationary state) differ from the conditions of the application voltage necessary to move the particles starting of moving. The voltage application time (pulse width) of a certain extent is necessary to move the particles in the stationary state. For example, with regards to the particles having a particle diameter of φ15 μm, the pulse width of about a few msec is required to sufficiently start the movement of the particles in the stationary state, and the particles may not be moved at the pulse width of less than or equal to 1 msec (frequency of greater than or equal to 500 Hz). Applying plural pulse voltages is effective in increasing the display density, but the display switching time increases significantly if the number of pulse of a few msec increases.